SUNDAY, May 2 (HealthDay News) -- About one in five children with autism uses alternative treatments to help with the neurodevelopmental disorder, most often a special diet, a new study finds.

Of 1,212 children with an autism spectrum disorder included in the study, about 17% were on special diets. More than half of those were on a gluten-free, casein-free diet, which eliminates wheat and dairy products. Other common dietary changes included avoiding processed sugars and taking probiotics, microorganisms found in foods such as yogurt and supplements that may help maintain gut bacterial flora.

"People turn to complementary and alternative treatments anytime they perceive conventional medical treatments as either not doing the job or being too expensive, or that the complementary and alternative treatments are more natural," said Dr. Daniel Coury, medical director of the Autism Treatment Network and a professor of pediatrics and psychiatry at Ohio State University. "We see the same sorts of reasons among children on the spectrum."

The study was to be presented Sunday at the Pediatric Academic Societies' annual meeting in Vancouver, British Columbia, Canada.

Other alternative treatments parents reported trying for their kids ran the gamut from hyperbaric oxygen, which involves pressurized chambers with oxygen-rich air that usually are used to treat divers with the bends, to chelation therapy, a treatment that removes heavy metals from the body. That treatment stemmed from fears that mercury causes autism, Coury said.

Despite significant publicity about the methods, less than 1% of parents had tried them, the study found. And that's a good thing, Coury said, because there's no evidence that either works and some evidence that they might be dangerous.

Parents might be turning to special diets because of reports that autistic children are more prone to gastrointestinal (GI) problems. Though earlier studies have had mixed results about the prevalence of GI issues, a second study also slated for presentation at the meeting found that parents reported GI symptoms in nearly half of the children.

For that study, families of 1,185 children enrolled in the Autism Treatment Network filled out questionnaires about GI symptoms, behavior, sleep and quality of life.

About 45 percent reported their children had GI symptoms, such as abdominal pain, constipation and diarrhea. The problems were more common as children got older, affecting about 9 percent of children younger than 5 and 51 percent of children 7 and older.

Their symptoms were bad enough to affect the quality of their lives, with about 70 percent of children with GI symptoms having sleep problems, compared with 30 percent who didn't have GI issues, the study found.

Kids with GI issues also have more behavioral issues, possibly because of their lack of sleep, suggests a third study from the meeting, which included 1,056 children in the Autism Treatment Network. It found an association between sleep problems and behavioral issues that included emotional problems and anxiety.

Autism is a complex disorder, and parents are driven by the desire to help their children, said Dr. Paul Law, director of the Interactive Autism Network at the Kennedy Krieger Institute in Baltimore. He said he's seen hundreds of alternative treatments tried by parents: supplements and vitamins, acupuncture, acupressure, bathing in distilled water and various types of animal therapy, among them. One mother, Law said, had tried 68 different methods.

Though it's not hard to find testimonials about the effectiveness of one treatment or another, medical evidence that they work is scanty, and the placebo effect can be powerful, Law said.

"There is an adage in medicine that the more you don't know about how to treat something, the more treatments there are," Law said, noting that medications can treat some of the symptoms of autism, but no medication treats the autism itself.

Coury agreed. "For the majority of these treatments, there is no good research to support their effectiveness," he said.

Treatments that have been shown to work include behavioral interventions and medications that can help curb aggressive and other behavioral issues, Law said.

About 27 percent of children with an autism spectrum disorder are taking at least one medication to manage their behavior, according to a fourth study from the meeting. It found that the most common reasons for medication use were hyperactivity, repetitive behaviors, irritability and problems with attention.

Of the children taking medications, nearly half were taking two or more medications.

Medication use became more common as children got older, the study found. About 60 percent of children aged 11 and older took medication, compared with 44 percent of children aged 6 to 10, 11 percent of children aged 3 to 5 and 4 percent of kids younger than 3.

About one in 110 U.S. children has autism, which is characterized by difficulties with social, language and communications skills and restricted or repetitive behaviors or interests.

The Autism Treatment Network, run by Autism Speaks, a New York-based research and advocacy organization, includes 14 treatment and research centers in the United States and Canada for children with autism who are 2 to 18 years old.